Linking scales of flow variability to lotic ecosystem structure and function

Biggs, B. J. F., Nikora, V. I., & Snelder, T. H. (2005). Linking scales of flow variability to lotic ecosystem structure and function. River Research and Applications, 21(2-3), 283-298.

While biotic interactions have major influences on ecosystem, Biggs et al. argue that the abiotic environment constrains the biotic interactions playing a greater role in ecosystem. "An organism must be able to survive, grow and reproduce under a given set of abiotic conditions, before the habitat defined by those conditions can be considered viable for that species."  Abiotic conditions are the non-living chemical and physical factors in the environment as opposed to the biotic which is the living component of a community. Over evolutionary time species gradually adapt to specific habitats both abioticly and bioticly .  These abiotic environments act as evolutionary forces that drive the development of different sets of traits.  These forces are not static, and are extremely variable in both time and space. These forces can be climatic such as rain, wind, flooding, and flow variability.

Biggs et. al, punished work in River Research and Applications (River Res. Applic. 21: 283–298, 2005) linking flow variability to the lotic ecosystem structure and function.  Having a study area of New Zealand and focusing on rivers with a ranging difference in flow variability, they show that temporal variations in flow strongly influences the functional processes and structures of lotic ecosystems. They hypothesized that the lotic ecosystem is sensitive to flow variability at temporal scales, but also sensitive on scale of magnitude. They show that "infrequent, but high magnitude flow variations influence lotic ecosystem structure and function at high system levels (i.e. communities) through drag processes (resulting in ‘drag-disturbance’) whereas more frequent, but lower magnitude events influence ecosystem structure and function more through mass-transfer processes (controlling growth of individuals)."

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While this reserached focuses on New Zealand, this concept of climatic senstivity in lotic ecosystems is critical in the age of climate change.  As with the Rivers in New Zealand, many rivers have variations in flow that is controlled by inter-annual variations in climate.  Year to year variations in New Zealand are driven by two Oscillations, the El Nino Southern Oscillation (ENSO) phenomenon superimposed by the Interdecadal Pacific Oscillation (IPO).  During El Nino there tends to be greater precipitation and higher more frequent flow events in the south and west of new Zealand. These inter-annual variations in flow regime have major implications river ecosystems due to the frequent flood disturbances in come years, and low flows in other years.  The figure below from the article shows the hydrograph of three rivers in New Zealand, where the inter-annual variation is apparent with the peaks in flow rates. The Bottom Chart is they hydrograph from the source of the two river above, while the source is relatively stable, down stream there is a strong variations related to runoff from storm events.

Biggs et. al. believes that ecological effects of horological variability follow a hierarchically principles, with effects of flow variation on communities by large scale events and event effects at lower levels with smaller scale flow variations.  They hypothesize that flow variability is the underlying reason for the temporal and spatial patterns of biological characteristic are different scales in the lotic ecosystem.

They conclude that "high energy flow events are generally catastrophic to lotic ecosystem structure and function for periods of time that vary depending on the resistance and resilience of the different populations."

Find it Online
Wiley Online Library - http://onlinelibrary.wiley.com/doi/10.1002/rra.847/abstract